Currently, it is anticipated that the North American Numbering Plan (NANP) will reach exhaustion in the near future, perhaps as early as the year 2007. The NANP uses a 10 digit telephone number format for end user network addresses, i.e. telephone numbers, and eventually continued growth of the telephone network will exhaust the NANP, making it necessary to enlarge the telephone number format. This change will have a major impact. Everything that uses a telephone number will be affected. Major expenditures to accommodate the new format will be required worldwide. All countries using NANP must agree to the new format and to a transition method. Various national regulators must then order the agreed solution and then years will be required to implement the necessary hardware changes. Even the cutover period may be spread over an extended interval. While it is important to decide as soon as possible how the NANP expansion will be accomplished, it is also important to defer actually implementing the expansion as long as possible. The present value of the expansion's cost shrinks the longer the expansion can be delayed and the actual cost can actually be reduced since the changes required to implement the NANP expansion can be included in the normal modernization of equipment.
While the growth in use of the network drives the exhaustion of the NANP and is expected to reach a point where more than the 10 billion currently possible numbers will be needed, inefficiencies in the way numbers are assigned will hasten that date. Particularly, the use of numbers in the NANP to identify not just particular stations on the network but also the geographical area where the stations are actually located; and the manner in which numbers are assigned to particular geographical areas, can result in numbers being “stranded” in low-growth areas where they are unlikely to be assigned to an end user in the foreseeable future. An extreme example of this problem occurs in one area code where the assignee of the present invention uses approximately 7% of the numbers assigned.
A rate area is a geographic area represented by a single point, the “rate center”. The rate center is used to represent the physical location of all end users located within the rate area. Distance is calculated between the calling station and the called station based on the rate centers associated with each station. Groups of rate areas form a station's calling area. Local calling plans for end users are usually defined as calls between certain pairs of rate areas. Rate areas determine whether inter-carrier settlements are done for local or toll traffic minutes. This is an important distinction as “toll” access minutes cost about 3 times as much as “local” traffic minutes. Rate areas are thus very important to local service providers. Currently, the first 6 digits of a 10 digit telephone number, hereinafter sometimes NPA-NXX, nominally indicate the rate area in which the identified rate station is located. Carriers comprised in the network rely on the NPA-NXX of a called telephone number to identify the called station's associated rate area and thus each NPA-NXX must correspond to only one rate area.
Typically, though not necessarily, the NPA-NXX of a number is also used to identify the switch serving the called station in order to route the call through the network, as will be described further below. Within a given area code (NPA) an office code (NXX) is assigned to a switch and to a rate area served by that switch. That is, the 10 thousand numbers defined by the last 4 digits are assigned by the network administrator to a particular switch and a particular rate area served by that switch. In rate areas that are growing slowly, or are served by a large number of carriers, assignment of numbers in blocks of 10 thousand can result in a large fraction of “stranded” numbers.
To address this problem a “thousand-block number pooling” method of number assignment has been implemented in the telephone switched network. Blocks of one thousand numbers are “ported” from the switch normally associated with an NXX to another switch serving the same rate area. This breaks the relation between NPA-NXX and the switch, and calls are routed based on pointers (LRN's) associated with the ported numbers in a database maintained by the network Administrator. It has recently been proposed to extend this approach to the porting of individual telephone numbers.
While the above described approaches to number assignment have proven to be somewhat effective in increasing the utilization of numbers in rate areas served by more than one switch, “number pooling” approaches still require that particular NPA-NXX's be associated with a single rate area with the result that large fractions of numbers assigned to low-growth areas can be stranded”. Consequently, there is a need for a number assignment method, and a network adapted to such a method, which will allow the assignment of “stranded” numbers without regard to rate areas in which stations are located, and thereby improve utilization of the NANP.